The main coloring component of hair is a dark pigment, melanin, which occurs as granules embedded in the hair cortex. The aim of bleaching is to decolorize selectively the natural pigments or applied pigments in the hair with minimal damage to the hair matrix. When hair is bleached, the color changes to lighter and lighter shades depending upon the amount of melanin granules dissolved and removed from the hair fiber. Hydrogen peroxide is the leading solvent for melanin used in the bleaching process; however, along with melanin removal, the peroxide reacts with keratin to cause loss of tensile properties and damage to the hair. More specifically, bleaching occurs in two steps: (1) initial solubilization of the color granules and (2) decolorization of the dark brown solubilized pigment. The reaction between melano-protein and hydrogen peroxide is confined mainly to the protein-combined cystene residues which are subsequently converted to combined cysteic acid. The solubilization of the melanin granules is connected with the splitting of the disulfide bridges in the melano protein and it is likely that the disulfide bridge may be the stabilizing factor in melanin, as it is in keratins.
The bleaching process can be halted at any point or can be permitted to continue to a light blonde or platinum shade. The latter provides a good background for a variety of tints which can be obtained by a subsequent coloring step. Such bleaching and coloring combination is known as a double process coloring and causes hair damage by promoting porosity, brittleness, loss of tensile strength and dryness.
Permanent hair colorants involve the use of oxidation dye intermediates which are colorless substances but which, when mixed with oxidizing agents just prior to use, produce color by a process of oxidative condensation. More specifically, the intermediates, in the presence of an oxidant, couple with another oxidation dye intermediate molecule to form a large fused ring color compound within the hair fiber. Since the fused ring product is too large to penetrate the hair fiber, it is essential that good penetration is achieved by the precursor intermediate. The oxidation dye process engenders many changes in the chemical and cosmetic characteristics of the hair which are undesirable. Specifically, the effect of alkali swelling of the hair fiber leads to loss of tensile strength, flexibility and promotes a porous, dry appearance. Additionally, the oxidation dye intermediates often cause skin sensitivity and reddening. Still further, the color imparted on processed hair is often non-uniform since the preprocessed sections, have higher porosity and absorb the interemediate at a faster rate than virgin growth which is more resistant to absorption.
Certain quaternized amine compounds and polymeric amines as disclosed in U.S. Pat. No. 4,532,127 and U.S. Pat. No. 4,579,732 have been developed to overcome some of the above problems. However these basic compounds have not been found to be completely satisfactory since they react with anionic components which are commonly present in hair coloring or bleaching compositions. This reactivity causes undesirable alterations in the shade desired. Additionally the amino groups react with hydrogen peroxide to form nitrogen oxides, thus increasing the effective amount of peroxide which must be employed in bleaching compositions. Since peroxides are known to have a drying effect on hair, it is desirable to use as little as possible to obtain the desired effect. Further the relatively high viscosity of the polymeric compounds together with the normal variation in molecular weight of the polymer chains in the product lead to formulation problems in reproducability of product quality and in storage of the product over extended periods. In addition the large molecular size of the polymeric products prevents their penetration into the hair fiber and instead forms a coating over the hair, which may develop tack under conditions of high humidity. Finally, many hair dye and bleaching compositions produce a disagreeable odor which the prior quaternized amino compounds do not mask.
Accordingly, it is an object of this invention to overcome or minimize the above deficiencies by providing a chemically stable additive which obviates skin sensitization, conditions the hair during processing, aids in the penetration of dye intermediate without undue alkaline swelling of the hair fiber, provides complexing sites on which the colorant can form, minimizes the period of hair exposure to chemical solutions, provides a more uniform distribution of color to processed hair by promoting penetration in portions of new hair growth, preserves the tensile properties of bleached or dyed hair and successfully masks undesirable thiol odors.
These and other objects of the invention will become apparent from the following description and disclosure.